Pennington Nutrition SeriesHealthier lives through education in nutrition and preventive medicine No. 47 Green Tea A Review of Potential Health Benefits Green tea is one of four types of tea (white, green, black, and oolong) that come from the plant Camellia sinensis. White tea is the least processed form of tea, while black tea leaves are fermented. Green tea leaves are steamed, not fermented and hence preserve more polyphenols. The beneficial effects of green tea are attributed to the polyphenols, particularly the catechins, which make up 30% of the dry weight of green tea leaves. These catechins are present in higher quantities in green tea than in black or oolong tea, because of the differences in the processing of tea leaves after harvest. Green Tea and Chronic Diseases Many studies have found beneficial effects associated with the consumption of green tea. In fact, green tea has been shown to play a beneficial role in six different areas: Cardiovascular diseases Obesity and weight loss Diabetes Cancer Tea has been consumed as a Microbial diseases beverage for thousands of years, first in the Orient and Neurodegenerative diseases then Europe and the Americas. — Aging Green tea has been used in oriental medicine because of — Parkinson’s disease its beneficial effects. — Alzheimer’s disease
ECCGGreen tea has polyphenolic catechins, of which (-)epigallocatechin—3—gallate (EGCG) is one of six. EGCG is the most abundant catechin,accounting for 65% of green tea’s catechin content, and seems toproduce most of the beneficial effects found in green tea. One cup ofgreen tea contains approximately 100-200 mg of EGCG. Othercomponents found in green tea include: caffeine, theanine, theaflavins,theobromine, theophylline, and phenolic acids such as gallic acid. Cardiovascular DiseaseOverview: Green tea polyphenols (catechins) are Diabetespotent antioxidants which reduce free radicaldamage to cells and prevent the oxidation of LDL Green tea consumption can alsocholesterol. Preventing oxidation of the LDL particle benefit diabetics. In a study oninhibits the formation of atherosclerotic plaques. human subjects, the consumptionTherefore the consumption of green tea is believed of green tea was shown to improveto be linked to a lower risk of heart disease. glucose tolerance. Basal blood glucose levels did not change. In a study of over 8,000 Japanese men and In laboratory animals, long-term women for 12 years, increased consumption of administration of green tea extract green tea was associated with greater health increased insulin sensitivity. benefits. In fact, those who consumed ~32 ounces a day over a 12 year period had a 58% In cell culture studies, EGCG was lower risk of dying from coronary heart disease the most active catechin in than those who consumed about ~10 ounces a increasing insulin sensitivity and day. glucose uptake in isolated fat cells. Consumption of black tea, which is notably lower in catechins, was also shown to provide significant benefits. In a 6-yr Dutch study of over 4,500 men and women, those who consumed more than 3 cups (~13 ounces a day) of black tea daily had a 68% lower risk of myocardial infarction (a heart attack) than those who did not drink tea. Therefore, even moderate amounts of tea consumption can potentially provide significant cardiovascular protection.
Cancer Neurodegenerative DiseasesIn the scientific world, green tea is probably best knownand most studied for its effects on cancer prevention. Free Radical Theory of AgingAlthough epidemiological studies have not shown a clear According to the free radical theory of aging,link between cancer prevention and green tea, animal increased free radical generation and oxidativestudies have been very convincing. They have clearly stress are the basis for changes that lead to agedemonstrated the preventative effects of green tea and -associated functional deterioration and neu-EGCG against liver, stomach, breast, prostate, lung and rodegeneration. Several age-associated dis-skin cancers at any stage (initiation, promotion or eases such as cancer, Parkinson’s disease,progression). Alzheimer’s disease, cardiovascular disease, and diabetes have their etiologies linked to freeTea catechins act as powerful inhibitors of cancer growth radical damage. Because of the antioxidantin several ways. They: properties of green tea and its extracts, several scavenge oxidants before cell injuries occur, studies have examined the effects of green tea reduce the incidence and size of chemically consumption on these age-related conditions. induced tumors, and inhibit the growth of tumor cells. Parkinson’s disease Oxidative stress, especially the death ofThe National Cancer Institute (NCI) has funded extensive dopaminergic neurons, is believed to be aresearch with green tea as a potential cancer major contributor to the pathogenesis ofchemopreventive agent. A study is underway to see the Parkinson’s disease. Recently, misregulatedchemopreventive effect of POLYPHENON E iron metabolism in the brain has also been(a decaffeinated green tea extract currently in Phase II implicated as a potential contributor. Severalclinical trials). studies using green tea have shown significant protection against the development of this disease. Because of its antioxidant and iron- chealating properties, EGCG was believed to be the protective agent responsible these results. Alzheimer’s disease Although there is currently no epidemiological evidence on the benefit of green tea for Alzheimer’s disease in humans, there have been several studies in laboratory animals andSome of the cancer preventive activity of green tea is cell cultures which suggest that EGCG may due to its antioxidant activity. Smoking increases delay this disease. oxidative damage in cells. In a study, smokers were Stroke encouraged to consume several cups of green tea In laboratory animals, EGCG had a significant each day. The consumption of green tea was antioxidant effect and protected againstassociated with decreases in the levels of 8-OHdG, a neurological deficits. marker of oxidative DNA damage in smokers.
Microbial DiseasesGreen tea has been known to prevent dental caries (cavities) by preventing theattachment of the bacteria associated with dental caries to the teeth. Green teaincreases the resistance of tooth enamel to acid induced erosion, and displaysanti-inflammatory properties by reducing gum disease (gingivitis).Recently, green tea has been successful in increasing antibiotic effectiveness inmulti-drug resistant Staphylococcus aureus infections. In addition, EGCG has beenshown to be effective in preventing HIV infection at the initial step in the HIV-1 infectionprocess. The Pennington Biomedical Research Center is a world-renowned nutrition research center. Mission: References To promote healthier lives through research and education in nutrition and preventive medicine. Cooper R, Morre J, Morre D. Medicinal Benefits of The Pennington Center has several research areas, including: Green Tea: Part I. Review of Noncancer Health Bene- fits. J Alternat Complement Med. 2005; 11(3): 521-28. Clinical Obesity Research Experimental Obesity Zaveri N. Green tea and its polyphenolic catechins: Medicinal uses in cancer and noncancer applications. Functional Foods Life Sciences. 2006; 78: 2073-2080. Health and Performance Enhancement Crespy V, Williamson. A review of the health effects Nutrition and Chronic Diseases of green tea catechins in in vivo animal models. Nutrition and the Brain J Nutr. 2004; 134: 3431S-3440S. Dementia, Alzheimer’s and healthy aging Pennington Nutrition Series No 47 9/07 Diet, exercise, weight loss and weight loss maintenance Authors The research fostered in these areas can have a profound impact on healthy living and Heli J. Roy, PhD, RD on the prevention of common chronic diseases, such as heart disease, cancer, diabe- tes, hypertension and osteoporosis. Shanna Lundy, MS Chad Eriksen, BA The Division of Education provides education and information to the scientific commu- nity and the public about research findings, training programs and research areas, and Beth Kalicki coordinates educational events for the public on various health issues. Division of Education We invite people of all ages and backgrounds to participate in the exciting research Phillip Brantley, PhD, Director studies being conducted at the Pennington Center in Baton Rouge, Louisiana. If you Pennington Biomedical Research Center would like to take part, visit the clinical trials web page at www.pbrc.edu or call (225) 763-3000. Claude Bouchard, PhD, Executive Director Edited : October 2009